1. Field of the Invention
This invention relates to engine control apparatuses that control engines of hybrid vehicles, and particularly to engine control apparatuses that stop and restart the engines as well as cut off fuel supply to the engines in hybrid vehicles installing automatic transmissions.
This application is based on Patent Application No. Hei 11-219359 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, hybrid vehicles are well known to install electric motors in addition to engines as driving sources. Generally, the hybrid vehicles are classified into two types of vehicles, namely, series hybrid vehicles and parallel hybrid vehicles. The series hybrid vehicles are designed to drive wheels by electric motors, which are driven by electric power generated by generators being driven by engines. The parallel hybrid vehicles are designed such that electric motors (or drive assist motors) are directly coupled to engines and assist to drive shafts of the engines. In addition, the parallel hybrid vehicles are equipped with generators, which are provided independently of the motors or which are actualized by the drive assist motors. So, electric energy generated by the aforementioned generators is accumulated in battery devices of the parallel hybrid vehicles.
The aforementioned hybrid vehicles are capable of running the engines with substantially constant engine speeds within prescribed engine speed zones realizing high fuel efficiency and low emission. Therefore, as compared with the conventional vehicles using only internal-combustion engines, the hybrid vehicles are capable of realizing good fuel efficiency and low emission in discharge gas.
Some of the hybrid vehicles (disclosed by Japanese Unexamined Patent Publication No. Hei 8-317505, for example) are designed to allow engine operations to be stopped under prescribed drive conditions.
The hybrid vehicles are capable of running in three modes, namely, an engine running mode, a motor running mode and an engine-and-motor running mode, in response to drive conditions thereof. So, the hybrid vehicles are superior in some advantages to cope with the drive conditions (e.g., stop conditions). For example, it is possible to avoid overcharge of batteries by automatically stopping engine operations, or it is possible to further improve fuel efficiency by adequately selecting the running modes. However, the hybrid vehicles suffer from the following problems.
That is, the hybrid vehicles employ automatic transmissions such as continuously variable transmissions (CVTs), oil pressures of which are secured by engine outputs. So, when the hybrid vehicles stop the engines without preparation of the automatic transmissions in starting, the automatic transmissions simultaneously loose controls thereof. Thus, the vehicles must be started with certain reduction ratios of the automatic transmissions which are established at engine stops, so that acceleration become slow (or dull). In addition, it takes a long time to accomplish perfect engagement of starting clutches. In that case, the hybrid vehicles suffer from a problem in that fuel efficiency is deteriorated.
Further, because a certain oil pressure is needed to restore a reduction ratio enabling start of the vehicle, lubrication shortage occurs on the starting clutch. Furthermore, there is a probability in that hydraulic pressure and lubrication cannot be sufficiently supplied to parts of the CVT.
It is an object of this invention to provide an engine control apparatus that is capable of stopping an engine of a hybrid vehicle after standby for waiting a start implementing condition to be established.
According to a first aspect of the invention, an engine control apparatus is applied to a vehicle in which wheels are driven by driving power being produced by an engine and transmitted by an automatic transmission (e.g., CVT). Herein, the engine control apparatus basically operates to enable automatic stop and restart of the engine in response to prescribed drive conditions of the vehicle. In addition, the engine control apparatus cuts off fuel supply to the engine at a deceleration mode of the vehicle. By detecting that the automatic transmission returns its reduction ratio to a restart-enable reduction ratio, the engine control apparatus allows execution of an engine stop. Thus, it is possible to prevent the engine stop from being executed before the automatic transmission is returned to the restart-enable reduction ratio.
According to a second aspect of the invention, an engine control apparatus is applied to a hybrid vehicle which installs an engine and a motor as driving power sources for driving wheels. The engine control apparatus basically operates to enable automatic stop and restart of the engine in response to prescribed drive conditions of the hybrid vehicle. In addition, the engine control apparatus cuts off fuel supply to the engine at a deceleration mode of the hybrid vehicle. Further, the engine control apparatus is equipped with a detector for detecting engine speed of the engine and a detector for detecting a reduction ratio of an automatic transmission (e.g., CVT). Herein, the reduction ratio is detected by calculating a ratio between an engine rotation speed and an output shaft rotation speed, for example. Furthermore, the engine control apparatus maintains an idle rotation speed of the engine by controlling the motor to rotate in response to the engine speed under execution of fuel cut at the deceleration mode until the automatic transmission is returned to a restart-enable reduction ratio. Thus, it is possible to prevent an engine stop from being executed before the automatic transmission is returned to the restart-enable reduction ratio under execution of the fuel cut at the deceleration mode. In addition, the vehicle does not restart after the engine stop with an extremely low reduction ratio of the automatic transmission, so it is possible to produce appropriate acceleration. Since the automatic transmission has been already returned to the restart-enable reduction ratio before restarting, it is possible to use hydraulic pressure of the automatic transmission exclusively for restarting the vehicle. So, it is possible to avoid occurrence of an unwanted situation where hydraulic pressure and lubrication are not sufficiently supplied to parts of the CVT.
According to a third aspect of the invention, the engine control apparatus controls the motor such that motor torque is increased in response to decrease of the engine speed when maintaining the idle rotation of the engine. So, it is possible to eliminate a feeling of wrongness for the driver when the motor torque is produced.